buffers - Node.js Manual & Documentation

## Buffers

Pure Javascript is Unicode friendly but not nice to binary data. When dealing with TCP streams or the file system, it's necessary to handle octet streams. Node has several strategies for manipulating, creating, and consuming octet streams.

Raw data is stored in instances of the `Buffer` class. A `Buffer` is similar to an array of integers but corresponds to a raw memory allocation outside the V8 heap. A `Buffer` cannot be resized.

The `Buffer` object is global.

Converting between Buffers and JavaScript string objects requires an explicit encoding method. Here are the different string encodings;

- `'ascii'` - for 7 bit ASCII data only. This encoding method is very fast, and will strip the high bit if set.

- `'utf8'` - Unicode characters. Many web pages and other document formats use UTF-8.

- `'base64'` - Base64 string encoding.

- `'binary'` - A way of encoding raw binary data into strings by using only the first 8 bits of each character. This encoding method is depreciated and should be avoided in favor of `Buffer` objects where possible. This encoding will be removed in future versions of Node.

### new Buffer(size)

Allocates a new buffer of `size` octets.

### new Buffer(array)

Allocates a new buffer using an `array` of octets.

### new Buffer(str, encoding='utf8')

Allocates a new buffer containing the given `str`.

### buffer.write(string, offset=0, encoding='utf8')

Writes `string` to the buffer at `offset` using the given encoding. Returns number of octets written. If `buffer` did not contain enough space to fit the entire string, it will write a partial amount of the string. In the case of `'utf8'` encoding, the method will not write partial characters.

Example: write a utf8 string into a buffer, then print it

    buf = new Buffer(256);
    len = buf.write('\u00bd + \u00bc = \u00be', 0);
    console.log(len + " bytes: " + buf.toString('utf8', 0, len));

    // 12 bytes: ½ + ¼ = ¾

### buffer.toString(encoding, start=0, end=buffer.length)

Decodes and returns a string from buffer data encoded with `encoding` beginning at `start` and ending at `end`.

See `buffer.write()` example, above.

### buffer[index]

Get and set the octet at `index`. The values refer to individual bytes, so the legal range is between `0x00` and `0xFF` hex or `0` and `255`.

Example: copy an ASCII string into a buffer, one byte at a time:

    str = "node.js";
    buf = new Buffer(str.length);

    for (var i = 0; i < str.length ; i++) {
      buf[i] = str.charCodeAt(i);
    }

    console.log(buf);

    // node.js

### Buffer.isBuffer(obj)

Tests if `obj` is a `Buffer`.

### Buffer.byteLength(string, encoding='utf8')

Gives the actual byte length of a string. This is not the same as `String.prototype.length` since that returns the number of characters in a string.

Example:

    str = '\u00bd + \u00bc = \u00be';

    console.log(str + ": " + str.length + " characters, " +
      Buffer.byteLength(str, 'utf8') + " bytes");

    // ½ + ¼ = ¾: 9 characters, 12 bytes

### buffer.length

The size of the buffer in bytes. Note that this is not necessarily the size of the contents. `length` refers to the amount of memory allocated for the buffer object. It does not change when the contents of the buffer are changed.

    buf = new Buffer(1234);

    console.log(buf.length);
    buf.write("some string", "ascii", 0);
    console.log(buf.length);

    // 1234
    // 1234

### buffer.copy(targetBuffer, targetStart=0, sourceStart=0, sourceEnd=buffer.length)

Does a memcpy() between buffers.

Example: build two Buffers, then copy `buf1` from byte 16 through byte 19 into `buf2`, starting at the 8th byte in `buf2`.

    buf1 = new Buffer(26);
    buf2 = new Buffer(26);

    for (var i = 0 ; i < 26 ; i++) {
      buf1[i] = i + 97; // 97 is ASCII a
      buf2[i] = 33; // ASCII !
    }

    buf1.copy(buf2, 8, 16, 20);
    console.log(buf2.toString('ascii', 0, 25));

    // !!!!!!!!qrst!!!!!!!!!!!!!

### buffer.slice(start, end=buffer.length)

Returns a new buffer which references the same memory as the old, but offset and cropped by the `start` and `end` indexes.

Modifying the new buffer slice will modify memory in the original buffer!

Example: build a Buffer with the ASCII alphabet, take a slice, then modify one byte from the original Buffer.

    var buf1 = new Buffer(26);

    for (var i = 0 ; i < 26 ; i++) {
      buf1[i] = i + 97; // 97 is ASCII a
    }

    var buf2 = buf1.slice(0, 3);
    console.log(buf2.toString('ascii', 0, buf2.length));
    buf1[0] = 33;
    console.log(buf2.toString('ascii', 0, buf2.length));

    // abc
    // !bc